Conventionally known as so-called positive-acting photosensitive materials, which become soluble upon exposure to actinic radiation when used in the production of lithographic plates, etc., are orthoquinone diazide compounds. This type of compounds have actually been used extensively in lithographic plate production and other applications. Examples of such orthoquinone diazide compounds are disclosed in, for example, U.S. Pat. Nos. 2,766,118, 2,767,092, 2,772,972, 2,859,112, 2,907,665, 3,046,110, 3,046,111, 3,046,115, 3,046,118, 3,046,119, 3,046,120, 3,046,121, 3,046,122, 3,046,123, 3,061,430, 3,102,809, 3,106,465, 3,635,709, and 3,647,443 and many other publications.
Use of these orthoquinone diazide compounds takes advantage of their property that when irradiated with actinic radiation, the compounds decompose to form five-membered-ring carboxylic acids and become soluble in alkaline solutions. However, there have been problems that the photodecomposition yields a nitrogen gas and this causes lifting of the original which was in intimate contact with the photosensitive layer, resulting in print blurring, and that the undecomposed orthoquinone diazide compound causes a coupling reaction during development.
On the other hand, for forming resist patterns for use in producing electronic devices such as semiconductor elements, magnetic-bubble memories, integrated circuits, etc., photoresists having sensitivity to ultraviolet or visible light have conventionally been put to practical use extensively. Photoresists are categorized into two types, negative and positive; negative photoresists are those in which the portions exposed to light become insoluble in developing solutions, whereas positive photoresists are those in which the exposed portions become soluble. Since the negative photoresists are superior in sensitivity to the positive photoresists and are also excellent in the properties required for wet etching, such as adhesion to substrate and chemical resistance, they were mainly used until recently. However, because the widths of the lines constituting resist patterns and the spaces between such lines have been reduced greatly with the recent trend toward higher packing density and higher integration for semiconductor elements and other electronic elements, and because dry etching has come to be used for etching the substrates, photoresists have come to be required to possess high resolution and good resistance to dry etching and, hence, the positive photoresists are presently being employed in most cases. Among the positive photoresists, those of the alkali development type based on alkali-soluble novolac resins are mainly used in the present-day processes because of their excellent sensitivity, resolution, and dry etching resistance. Examples of these alkali development type positive photoresists are described, for example, in J.C. Strieter, Kodak Microelectronics Seminar Proceedings, 116(1976).
However, as electronic devices are becoming increasingly sophisticated and made to have more functions recently, finer resist patterns are strongly desired in order to attain higher packing density and higher integration.
Under the above circumstances, photoresists sensitive to shorter-wavelength radiations are currently being developed, from the photoresists sensitive to g-beam radiation (436 nm) to those sensitive to i-beam radiation (365 nm) and further to those sensitive to deep-UV light (200-300 nm). However, since the orthoquinone diazide compounds used as photosensitive material in the conventional positive photoresists well absorb light in the deep-UV region and have poor photo-bleaching properties in this region, there has been a problem that use of deep-UV light as exposure light results in impaired resist pattern shapes.
In order to eliminate the above problem, several proposals have been made with respect to photosensitive compositions that are positive-acting without using an orthoquinone diazide compound. One of these is to use compounds having a 2-nitrobenzyl ester or 2,6-dinitrobenzyl ester group, as described in, for example, JP-B-56-2696 (the term "JP-B" as used herein means an "examined Japanese patent publication"); U.S. Pat. No. 4,551,416; J. Vac. Sci. Technol., Vol. 19, p. 1338 (1981); and J. Electrochem. Soc., Vol. 129, p. 2552 (1982) and Vol. 130, p. 1433 (1983). Another proposal is to use compounds having a 2-nitrobenzyl sulfonate or 2,6-dinitrobenzyl sulfonate group, as described in, for example, U.S. Pat. No. 4,554,238; Macromolecules, Vol. 21, p. 2001 (1988); and SPIE, Vol. 920, p. 67 (1988). The above-proposed compounds, however, also absorb light in the deep-UV region and do not undergo photo-bleaching, thus posing the same problem.
Proposed as a method for improving photo-bleaching properties in the deep-UV region is to use compounds having a 2-diazo-1,3-dione ##STR2## group, as described in, for example, IEEE Trans. Electron Devices, Vol. ED-28, p. 1300 (1981); SPIE, Vol. 771, p. 2 (1987) and Vol. 920, p. 51 (1988); J. Photopolym. Sci. Technol., Vol. 2, p. 392 (1989); U.S. Pat. Nos. 4,522,911, 4,601,969, 4,622,283, 4,624,908, 4,626,491, 4,752,551, 4,808,512 and 4,910,123; and JP-A-63-163340, JP-A-64-33543, JP-A-1-106034, JP-A-1-106035, JP-A-1-106036, JP-A-1-106037, JP-A-1-124849, JP-A-1-152451, and JP-A-1-188852 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). Although these compounds do show photo-bleaching properties in the deep-UV region, there are problems that these compounds themselves are apt to sublime during baking and that they are poor in the ability to prevent the unexposed areas from being dissolved by alkaline developing solutions.
Further, as a method for obtaining a positive pattern, use of photoresists employing substituted benzyl ester compounds of various kinds has been proposed in JP-A-1-140144. Such photoresists undergo a decarboxylation reaction upon exposure to light to thereby decrease the ability of the exposed areas not to be dissolved by alkaline developing solutions. The proposed photoresists, however, have a problem that the difference in solubility in alkaline developing solutions between exposed and unexposed areas is not sufficiently large.